chore(combinatorics/simple_graph): remove bad simp attribute (#6736)
chore(combinatorics/simple_graph): remove bad simp attribute (#6736)

As in https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/symmetry.20fails.20if.20simple.20graph.20is.20imported.





leanprover-community/mathlib,leanprover-community/mathlib